It's probably github's HEAD of operations-puppet refering to
“master”. However, operations-puppet does not have a “master” branch,
but is developed on the “production” branch.

Switching the branch on a github checkout makes things work [1].

Since I lack administration access on github, and cannot check/fix
myself ...
Chad, could you grant me access, or update HEAD on github's
operation-puppet?

[1]

christian@spencer 0 14:48:38
cwd: ~
git clone git@github.com:wikimedia/operations-puppet.git
Cloning into 'operations-puppet'...
remote: Reusing existing pack: 88763, done.
remote: Counting objects: 205, done.
remote: Compressing objects: 100% (201/201), done.
remote: Total 88968 (delta 94), reused 0 (delta 0)
Receiving objects: 100% (88968/88968), 70.32 MiB | 1.66 MiB/s, done.
Resolving deltas: 100% (61780/61780), done.
warning: remote HEAD refers to nonexistent ref, unable to checkout.

christian@spencer 0 14:49:28
cwd: ~
cd operations-puppet/

christian@spencer 0 14:49:33
cwd: ~/operations-puppet
git checkout production
Checking out files: 100% (2536/2536), done.
Branch production set up to track remote branch production from origin.
Switched to a new branch 'production'

Fixed.